1. Field of the Invention
The present invention relates to bioelectronic systems and more particularly, to electromyographic biofeedback systems.
2. Description of the Prior Art:
There are in the prior art, many systems which measure human muscle activity and provide an output signal which corresponds to the muscle activity. However, most of these prior art systems are limited in the range of operation and are basically digital in nature in that they do not provide any response below a preset threshold level. Therefore, the patient or the therapist gets no information relative to small muscle movements. In some cases, it is the small muscle movements which are most important since these are the movements which indicate the earliest signs of progress in rehabilitation.
Examples of the prior are threshold systems are U.S. Pat. No. 3,656,474 to Gentry, et al, and U.S. Pat. No. 3,657,646 to Zmyslowski, et al.
Another prior art electromyograph is shown by Gaarder, et al, in U.S. Pat. No. 3,641,993. Gaarder, et al, teaches an electromyograph in which the amplification system is non-linear and in fact is responsive to the logarithm of the peak value of the input signals representing human muscle activity. Gaarder, et al, includes a means to integrate the voltage representing muscle activity over a preset time interval. Because of the requirement for integration of the input voltage, the teaching of Gaarder, et al, is not appropriate for a real time biofeedback system. The patient must have an instantaneous response to any muscle activity. A delay which is required by an integration system will not give the patient the proper kind of feedback information for him to determine what was the cause of the signal which he received at any instant of time. Further, the logarithmic amplification of the input signal by the Gaarder, et al, system prevents a wide dynamic range of operation. The system distorts the rate of change of muscle activity in the higher voltage range. For example, the output frequency rate in the Gaarder, et al, system changes very little in the top portion of the range of muscle activity.
A biofeedback system, to operate effectively must provide an instantaineous signal to the human which can be translated by the brain into an indication of small muscle movement. For this reason, it is very important that an electromyographic biofeedback system be sensitive over a wide range of muscle activity. The response to a single muscle unit, the smallest measurable muscle unit, should be such as to provide the patient with an appropriate indication of muscle activity. Biofeedback of small muscle activity such as an indication of activity by a single muscle unit provides a very positive psychological effect on the patient in that the patient can hear or see a positive indication of progress in rehabilitation.
Also, it is very important to maintain a uniform sensitivity of the electromyographic biofeedback system over a wide range of muscle activity to provide the patient and the therapist with an accurate indication of progress in the rehabilitation.
Additionally, since most human systems, such as human hearing are logarithmic in nature, it is important that the external biofeedback system be linear to prevent distortion of the magnitude of the muscle activity signal to the human ear.
All of the prior art systems discussed have one or more deficiencies which are overcome by a linear electromyographic biofeedback system.